The sociological concept of social cohesion (most common and used) is related to a kind of state by which individuals remain united, integrated into a social group, or, simply, the state of cohesive integration of the social group.
For the existence of this state it is necessary that each individual has motivation, it can be of different natures, such as that caused by social coercion (of various types), by the rules of reciprocity, by collective consciousness, by solidarity and ontological needs .
We note that there is social cohesion when we have a group composed of individuals who share goals, actions, ideas and beliefs. It is this sharing that makes the group's existence possible. The inverse of social cohesion would be social disintegration, which would cause the consequent extinction of the social group.
It is social cohesion that enables organic (in complex societies) and mechanical (in simple societies) solidarities. Solidarity, in turn, expands social cohesion. In other words, an individual only collaborates with society, engaging in an economic activity, for example, because it is linked to the group and by collaborating it strengthens that connection in a state of reciprocity. Of course, this interest in collaborating is also the result of social constraints, such as legal determinations, the collective conscience that directs, to a large extent, the actions and thinking of individuals and the psychic need to live in groups.